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Transcript
CHAPTER 7 A TOUR OF THE CELL The Cell Theory • The basic unit of life • Cells come from cells Microscopes provide windows to the world of the cell • 17th century – cells observed through microscope (CYTOLOGY) Microscopy: History Simple Compound Microscopy: History Microscopy: History Goals of Microscopy Produce a magnified image of the specimen (Magnification) Separate the details in the image (Resolving Power) Render the details visible to the human eye or camera. Magnification • Magnification - ratio of an object’s image to its real size Onion – 40X Onion – 1000X Resolving power Resolving power is a measure of image clarity. –It is the minimum distance two points can be separated and still viewed as two separate points. – It is determined by the wavelength of light used 0.2mm 0.1nm Enhancing Light Microscope Images • Electron microscope (EM) -focuses a beam of electrons through the specimen or onto its surface • Can study only DEAD CELLS! • Transmission electron microscopes (TEM) are used mainly to study the internal ultrastructure of cells (2D). Fig. 7.2a (Rabbit Trachea) • Scanning electron microscopes (SEM) are useful for studying surface structures (3D). Fig. 7.2b Gravitational Biology Facility (GBF) Cell biologists can isolate organelles to study their functions • Cell fractionation - separate the major organelles of the cells so that their individual functions can be studied. Fig. 7.3 • Ultracentrifuge- a machine that can spin at up to 130,000 revolutions per minute and apply forces more than 1 million times gravity (1,000,000 g). 1) Homogenization- disrupt the cell and release its contents. 2) Spin homogenate in a centrifuge. 3) Heavier pieces will separate into the pellet while lighter particles remain in the supernatant. 4) Repeat at higher speeds and longer durationssmaller and smaller organelles can be collected in subsequent pellets. Prokaryotic and Eukaryotic cells All cells have: • Plasma membrane. • Cytoplasm • Chromosomes • Genes, DNA • Ribosomes, (make proteins using the instructions contained in genes) The prokaryotic cell The Eukaryotic cell Prokaryotes • • • • No nucleus, ‘naked’ DNA No membrane bound organelles Cell wall has peptidoglycan Smaller in size (1-10um) Eukaryotes • Nucleus bound by a membrane • Membrane Bound Organelles • No peptidolycan in cell wall of plants • Upto 10 times larger (10100um) • More complex Similarities: -Both have Ribosomes -Are both covered by plasma membrane! -Both have DNA -DNA-> mRNA -> Protein (universal genetic code) Fig. 7.7 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 7.8 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • The plasma membrane functions as a selective barrier that allows passage of oxygen, nutrients, and wastes • Made up of phospholipids and proteins Nucleus (5 microns) Contains most of the genes Nuclear Membrane (double) covers it Pores in Nuclear Membrane (why?) Nucleolus – rRNA is sythesized here Chromatin is inside nucleus (DNA+protein) Chromosomes (46) Nucleus Function: Stores genes (DNA) Makes mRNA and other types of RNA Ribosomes Made up of rRNA and Protein Located ‘free’ in cytoplasm or in association with ER/ nuclear membrane (‘bound’) Function – Protein synthesis ‘benches’ Proteins made on Free ribosomes – these proteins stay in cytoplasm Proteins made on Bound ribosomes – proteins are located in the Plasma Membrane or exported out of the cell Endomembrane System Nuclear Envelope Endoplasmic Reticulum Golgi apparatus (or body) Lysosomes Vacoules Plasma Membrane Endoplasmic Reticulum What cell has a lot of RER? Made of sacs - cisternae -Cells involved in synthesis of enzymes for digestion ex: pancreas cellSmooth has a lot ER of SER? 2What types: and Rough ER-Cells involved in detoxification - in a alcoholic! -Cells making steroid hormones! Smooth ER functions: Lipid synthesis, glucose metabolism, detoxification of drugs (alcohol), muscle contraction Rough ER functions: Proteins fold in cisternae, some proteins are modified; plasma membrane proteins and phospholipids are synthesized Transport Vesicles Pinch off from the ER and contain the macromolecules being transported to the Golgi apparatus Golgi Apparatus Made of sacs – cisternae; cis side- receiving, trans side – news vesicles bud off Functions: Tags (attaches chemical groups), sorts, and packages macromolecules (warehouse) Lysosomes membrane-bounded sac of hydrolytic enzymes that digests macromolecules; low pH (5) inside lysosome protects the cell - how? Functions: Phagocytosis-In Amoeba – digestion of food vacoules Autophagy - recycling of cells own macromolecules (suicide bags) Destroy bacteria, viruses – in WBC Vacuoles Vesicles and vacuoles (larger versions) are membrane-bound sacs with different functions. Food vacuoles, fuse with lysosomes during phagocytosis Contractile vacuoles, pump excess water out of the cell (amoeba) Central vacuoles are found in many mature plant cells – stores water, salts, proteins, defensive compounds, pigments, metabolic byproducts Mitochondria and chloroplasts are What cell has a lot of Mitochondria? the main transformers of cells -Cells needing aenergy lot of ATP - heart muscle cell (for pumping), and liver cell (synthesis) Chloroplast • Found only in photosynthetic organisms (plants, some primitive eukaryotes) • Site for photosynthesis (makes glucose) • Has its own DNA • Has its own ribosomes • Has a double outer membrane Mitochondria • Found in plants and animals • Converts macromolecules into usable energy – ATP (site for cellular respiration) • Has its own DNA • Has its own ribosomes • Has a double outer membrane • Is semi-autonomous Peroxisomes generate and degrade H2O2 – Peroxisome has catalase that converts H2O2 to water; detoxify alcohol and other harmful compounds Cytoskeleton • Network of fibers extending throughout the cytoplasm • Provides mechanical support and maintains shape • Provides anchorage for many organelles and enzymes • Is dynamic - dismantling in one part and reassembling in another to Movement of organelles Movement of cilia, flagella, muscles • 3 main types of fibers in the cytoskeleton: Microtubules, Microfilaments, and Intermediate filaments. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings 1) Microtubules – made of tubulin (protein) • They grow or shrink as more tubulin molecules are added or removed. • Move chromosomes during cell division • Guide organelles • Are part of centrioles – (important to cell division) • Make up cilia and flagella 2) Microfilaments (Actin) Fig. 7.26 The shape of the microvilli in this intestinal cell are supported by microfilaments, anchored to a network of intermediate filaments. -Support -Muscle contraction -Amoeboid movement -Cytoplasmic streaming 3) Intermediary filaments - cell shape, organelle location Plant cells are encased by cell walls • Microfibrils of cellulose embedded in a matrix of proteins and other polysaccharides. Extracellular matrix (ECM) of animal cells COLLAGENglycoprotein Intracellular junctions help integrate cells • Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact. • Plant cells are perforated with plasmodesmata, channels allowing cysotol to pass between cells. • Animal Cells: Fig. 7.30 A cell is a living unit greater than the sum of its parts – Macrophages use actin filaments to move and extend pseudopodia, capturing their prey, bacteria. – Food vacuoles are digested by lysosomes, a product of the endomembrane system of ER and Golgi. • The enzymes of the lysosomes and proteins of the cytoskeleton are synthesized at the ribosomes. • The information for these proteins comes from genetic messages sent by DNA in the nucleus. • All of these processes require energy in the form of ATP, most of which is supplied by the mitochondria. • A cell is a living unit greater than the sum of its parts. Fig. 7.31